Study On Natural Ventilation Of Urban Tunnel With Upper Vents

Urban tunnel with the features of shallow depth and short length, was considered setting up the openings at many locations on roof of the tunnel, using the natural pressure at the gateway and the opening location that shall be formed due to traffic wind force produced by vehicle movement, to exhaust polluted air and get fresh air through the upper vents along the tunnel, the pollution of environment in the outlet can be alleviated, and the normal operation without electricity, cut down the cross section height of the tunnel and save the cost which is by the tunnel's construction and operation. With significant economy, this model has been gradually realized in the country. At present, the domestic approach to this research already have some results, particularly which is about the experiments and theoretical of the study. But how to design and evaluate it reasonable, the specification and results are limited. Therefore, basing on the existing theory research, natural ventilation with the top opening of the urban tunnel are simulated using the software SES in this study.SES (Subway Environment Simulation Input Manager) was used to establish one-dimensional mathematical model about natural ventilation with the openings at the top of the one-way urban tunnel. Analysis in normal traffic conditions, air pressure and hot pressure effect of natural ventilation. The results showed:IN normal traffic conditions, the influence of natural ventilation hot-pressing smaller, analysis of the effect not consider when hot-pressing.Under the conditions of the normal vehicles running in the tunnel and the same size and quantity of the openings, the flow of the tunnel airstream and the distribution of the concentration of harmful gases was obtained and discussed by changing the disposal fashions of the openings, the distance between both ends and the inner distance between two openings of the group. Under the conditions of the normal vehicles running in the tunnel and the same openings quantity and the distance between both ends and the inner distance between two openings of the group, the flow of the tunnel airstream and the distribution of the concentration of harmful gases was also obtained and discussed by changing the opening size. Then under the same total size of the openings, the same distance between both ends and the inner distance between two openings of the group, the flow of the tunnel airstream the distribution of the concentration of harmful gases was also obtained and discussed by changing the quantity of the openings. The results showed:The urban tunnel with openings can exhaust polluted air along the tunnel. In the same size and quantity of the openings, a group of five openings or six openings is the best ventilation style. The flow of the tunnel airstream will decrease with the increase of the distance between both ends and the inner distance between two openings of the group; The flow of the tunnel airstream will increase with the increase of the size of opening; In a certain area of the total holes, ends of the distance, he distance between two openings of the group, the flow of the tunnel airstream will first increase then decrease with the increase of the quantity of the openings.At last, the software STAR-CD was used to establish three-dimensional mathematical model; And the moving mesh technology was used to simulate and analyze the tunnel air flow in three-dimension. Then the characteristic of the air flow through the openings was obtained.Through the study, we come to the ventilation rule about natural ventilation with the openings at the top of urban tunnel and provide theoretical basis and technical basis for rational natural ventilation program in engineering practice.